Hashed Global Names

Hashed Global Names

The system will generate shorter global names if you set the USEEXTENTSET parameter to the value 1. (The default value for this parameter is 0, meaning use the standard global names.) These shorter global names are created from a hash of the package name and a hash of the class name, followed by a suffix. While the standard names are more readable, the shorter names can contribute to better performance.

When you set USEEXTENTSET to 1, each index is also assigned to a separate global, instead of using a single index global with different first subscripts. Again, this is done for increased performance.

To use hashed global names for the GlobalsTest.President class we defined earlier, we would add the following to the class definition:

/// Use hashed global names
Parameter USEEXTENTSET = 1;

After deleting the storage definition and recompiling the class, we can see the new storage definition with hashed global names:

Storage Default
{
...
<DataLocation>^Ebnm.EKUy.1</DataLocation>
<DefaultData>PresidentDefaultData</DefaultData>
<ExtentLocation>^Ebnm.EKUy</ExtentLocation>
<IdLocation>^Ebnm.EKUy.1</IdLocation>
<Index name="DOBIndex">
<Location>^Ebnm.EKUy.2</Location>
</Index>
<Index name="IDKEY">
<Location>^Ebnm.EKUy.1</Location>
</Index>
<Index name="NameIndex">
<Location>^Ebnm.EKUy.3</Location>
</Index>
<IndexLocation>^Ebnm.EKUy.I</IndexLocation>
<StreamLocation>^Ebnm.EKUy.S</StreamLocation>
<Type>%Storage.Persistent</Type>
}

Notice, in particular, the following storage keywords:

• The ExtentLocation is the hashed value that will be used to calculate global names for this class, in this case, ^Ebnm.EKUy.

• The DataLocation (equivalent to the IDKEY index), where class data will be stored, is now the hashed value with a “.1” appended to the name, in this case, ^Ebnm.EKUy.1.

• Each index now has its own Location and thus its own separate global. The name of the IdKey index global is equivalent to the hashed value with a ”.1” appended to the name, in this example, ^Ebnm.EKUy.1. The globals for the remaining indexes have “.2” to “.N” appended to the name. Here, the DOBIndex is stored in global ^Ebnm.EKUy.2 and the NameIndex is stored in ^Ebnm.EKUy.3.

• The IndexLocation is the hashed value with “.I” appended to the name, or ^Ebnm.EKUy.I, however, this global is often not used.

• The StreamLocation is the hashed value with “.S” appended to the name, or ^Ebnm.EKUy.S.

After creating and storing a few objects, the contents of these globals might look as follows, again using the Terminal:

USER>zwrite ^Ebnm.EKUy.1
^Ebnm.EKUy.1=3
^Ebnm.EKUy.1(1)=$lb("","Washington,George",1732,"1")
^Ebnm.EKUy.1(2)=$lb("","Adams,John",1735,"2")
^Ebnm.EKUy.1(3)=$lb("","Jefferson,Thomas",1743,"3")
 
USER>zwrite ^Ebnm.EKUy.2
^Ebnm.EKUy.2(1732,1)=""
^Ebnm.EKUy.2(1735,2)=""
^Ebnm.EKUy.2(1743,3)=""
 
USER>zwrite ^Ebnm.EKUy.3
^Ebnm.EKUy.3(" ADAMS,JOHN",2)=""
^Ebnm.EKUy.3(" JEFFERSON,THOMAS",3)=""
^Ebnm.EKUy.3(" WASHINGTON,GEORGE",1)="" 

USER>zwrite ^Ebnm.EKUy.S
^Ebnm.EKUy.S=3
^Ebnm.EKUy.S(1)="1,239"
^Ebnm.EKUy.S(1,1)="George Washington was born to a moderately prosperous family of planters in colonial ..."
^Ebnm.EKUy.S(2)="1,195"
^Ebnm.EKUy.S(2,1)="John Adams was born in Braintree, Massachusetts, and entered Harvard College at age 1..."
^Ebnm.EKUy.S(3)="1,202"
^Ebnm.EKUy.S(3,1)="Thomas Jefferson was born in the colony of Virginia and attended the College of Willi..."

For classes defined using an SQL CREATE TABLE statement, the default for the USEEXTENTSET parameter is 1. For more information on creating tables, see Defining Tables.

For example, let’s create a table using the Management Portal (System Explorer > SQL > Execute Query):

CREATE TABLE GlobalsTest.State (NAME CHAR (30) NOT NULL, ADMITYEAR INT)

After populating the table with some data, we see the globals ^Ebnm.BndZ.1 and ^Ebnm.BndZ.2 in the Management Portal (System Explorer > Globals). Notice that the package name is still GlobalsTest, so the first segment of the global names for GlobalsTest.State is the same as for GlobalsTest.President.

Using the Terminal, the contents of the globals might look like:

USER>zwrite ^Ebnm.BndZ.1
^Ebnm.BndZ.1=3
^Ebnm.BndZ.1(1)=$lb("Delaware",1787)
^Ebnm.BndZ.1(2)=$lb("Pennsylvania",1787)
^Ebnm.BndZ.1(3)=$lb("New Jersey",1787)
 
USER>zwrite ^Ebnm.BndZ.2
^Ebnm.BndZ.2(1)=$zwc(412,1,0)/*$bit(2..4)*/

The global ^Ebnm.BndZ.1 contains the States data and ^Ebnm.BndZ.2 is a bitmap extent index. See Bitmap Extent Index.

If we wanted to use standard global names with a class created via SQL, we could set the USEEXTENTSET parameter to the value 0:

CREATE TABLE GlobalsTest.State (%CLASSPARAMETER USEEXTENTSET 0, NAME CHAR (30) NOT NULL, ADMITYEAR INT)

This would generate the standard global names ^GlobalsTest.StateD and ^GlobalsTest.StateI.